Variable Bitrate Audio Only

I've been asked to set up a live HLS stream delivering 3 AAC streams of different bandwidths (no video) in a single .m3u8 container. The encoding is working fine, and I'm able to connect to the individual streams, but I can't figure out how to proceed. What's the best way to do this?

For adaptive bitrate switching to work, all the various bitrate renditions need to be keyframe aligned, some encoders offer a multi-bitrate encoding option, but the Wowza Transcoder AddOn is the most accurate way to create the ABR set.

For this reason ABR for true audio only is not possible as there are no keyframes in an audio only stream. However, you can transrate the audio, and use PassThru for the video and ABR should work. You will need to have a video track included.
It can be very low bitrate and empty and be set to PassThru, but it needs to be included for ABR to work. Audio only ABR is not supported.